The present invention generally relates to bicycle rear derailleurs and more particularly to a bicycle rear derailleur with a damper assembly.
It is known that a bicycle derailleur performs shifting operations by shifting the chain between a plurality of adjacent sprockets of a sprocket assembly of a bicycle. A further, also very important function of the derailleur is to ensure sufficient chain tension. For this purpose, a bicycle derailleur generally has the following structure. A base member is mounted on the bicycle. Furthermore, a movable member is movably coupled to the base member and a chain guide assembly is movably coupled to the movable member with respect to rotation about a rotational axis. The movable member is movable in the lateral (axial) direction to move the chain guide assembly between the sprockets of the sprocket assembly so that the chain may be shifted from an initial sprocket to a target sprocket. The chain guide assembly is biased in a rotational direction rotation by a torsion spring or the like, namely in the direction of tensioning of the bicycle chain which is guided by the chain guide, to maintain the chain in the tensioned state or to restore the tensioned state after a prior state of insufficient chain tensioning. This rotational or pivoting direction is also referred to as “chain tensioning direction.” A rotation of the chain guide in this direction increases the chain tension and, at the same time, reduces the tension of the torsion spring acting on the chain guide assembly. Depending on the current sprocket of the sprocket assembly with which the chain is engaged at a given point, the chain guide assembly will take various rotational positions relative to the movable member with regard to the rotational axis.
Impact on the chain and the chain guide assembly not only result from shifting of the derailleur by shifting the chain between various sprockets of the sprocket assembly, but also from riding itself. For example, when riding on uneven surfaces, the derailleur and the chain are subject to blows and vibrations which may act on the chain guide assembly in a rotational direction opposite to the “chain tensioning direction.” A rotation of the chain guide assembly in the direction opposite to the “chain tensioning direction” increases the tension of the torsion spring that acts on the chain guide, and directly results in a reduction in the chain tension, or at least results in a greater risk of a subsequent reduction of the chain tensioning below the necessary level. Negative effects may be a drop in the chain tensioning with unwanted slackness or “dangling” of the chain. In a worst case, the chain may fall off the sprocket assembly.
In order to counter such problems, conventional solutions are provided with a damper assembly that provides a resistance to rotational movement of the chain guide assembly in the rotational direction of the chain guide assembly opposite to “chain tensioning direction.” In this respect, the known solutions each have a one-way clutch and a friction device, which act together in such a way that the resistance regarding the rotational movement of the chain guide assembly is affected in a rotational direction opposite to the “chain tensioning direction.”
The movable member and the chain guide assembly may be rotated relative to each other, but are frictionally coupled via the friction device and the one-way clutch assembly, which due to the characteristics of the one-way clutch is only effective in the rotational direction opposite the “chain tensioning direction,” so that a dynamic friction is only present in this rotational direction to act against the rotation. In the other rotational direction corresponding to a backwards rotation of the chain guide in the sense of a tensioning chain, the chain guide assembly is decoupled from the movable member due to these one-way clutch characteristics, so that the tensioning of the chain by rotating the chain guide assembly encounters no resistance or at least only an irrelevant degree of resistance.
Such a derailleur is disclosed in DE 10 2007 040 156 A1. The derailleur includes a damper assembly having a friction device including a plurality of axially supported friction washers. A one-way roller clutch assembly is disposed radially outwardly of these friction washers in the same axial area, which results in the necessity of a relatively large dimension for the movable member in the radial direction. An advantage of this known solution is an adjustment unit having an exposed adjustment nut for adjusting the friction engagement and thus the damping force acting as resistance. This configuration allows the rider to adjust the damping force. However, for such an adjustment a tool is required and the question arises if an average rider has the necessary knowledge to adjust the damping force correctly. Further, the exposed adjustment nut is not protected from undesired rotation which may result in undesired adjustment of the damping force.
Other bicycle rear derailleurs with damper assemblies are disclosed in DE 10 2011 114 699 A1, which also use one-way roller clutches. The rotational axis of the chain guide assembly serves as an inner clutch member of the roller clutch. The friction device includes a leaf spring encircling an outer clutch member of the roller clutch and having two end portions radially protruding between the two rotational cams or alternatively between an adjustment screw and a rotational cam, which serve to adjust a basic friction and to control a momentarily acting friction via a control lever or the like, so that the bicyclist—according to his wishes, for example when riding on different terrain—may select the momentarily acting friction and thus the momentarily acting damping force by the control lever which is movable between two index positions. Providing the bicyclist with such a choice calls for a relatively high mechanical effort.
DE 19 2013 001 952 A1 discloses a rear derailleur that includes a sleeve-like friction element extending circumferentially around the roller clutch assembly and having a tapered or conical outer surface. The rotational axis rotatably supporting the chain guide assembly forms the inner clutch member of the roller clutch assembly.
EP 0 031 215 B1 discloses several different embodiments of a bicycle rear derailleur with a damper assembly. Generally, the damper assembly includes a one-way ratchet clutch and a friction device having axially arranged friction surfaces.